Generally, various ships such as a bulk carrier, a container ship, a passenger ship, or the like, have employed a fuel supply system using heavy oil (HFO or MDO) such as a bunker C oil, that is a liquid fuel, as propulsion fuel.
In the existing fuel supply system, if heavy oil, or the like, used as fuel combust, it causes serious environmental pollution due to harmful substances included in exhaust gas. Since a demand for preventing environmental pollution is increasingly regulated throughout the whole world, regulations for a propulsion system using heavy oil as fuel oil have also been reinforced. As a result, costs have been continuously increased in order to meet these regulations.
In addition, when oil prices increase due to factors such as depletion of fossil fuel, localized insecurity, or the like, several operational problems such as the rapid increase of fuel expenses of a ship using heavy oil as fuel, etc., are caused.
Therefore, research into a fuel supply system, etc., using clean fuel such as LNG (or, LPG, CNG, DME, etc.), that is a liquefied or gaseous fuel without using heavy oil (or, MDO) or instead of using a minimum amount of heavy oil, as fuel oil of various ships, mainly using LNG (or, LPG, CNG, DME, etc.) as fuel when heavy oil (or MDO) is expensive or standards required for environmental protection are increased, and mainly using heavy oil (or, MDO) when heavy oil (or MDO) is cheap or environmental standards are weak has been continuously conducted.